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Device and method for monitoring an electrochemical gas sensor




Title: Device and method for monitoring an electrochemical gas sensor.
Abstract: An electrochemical gas sensor testing device that includes a test signal generator that generates a multiplexed signal that includes a first test signal that includes alternating current (AC) and is free from a direct current (DC) component and a second signal that includes a DC bias voltage, an electrochemical cell that includes a counter electrode, a sensing electrode, and an electrolyte, the counter electrode and the sensing electrode being in electrical communication with the electrolyte and each other, the counter electrode being in electrical communication with the signal generator to receive the multiplexed signal generated by the signal generator, and a processor that receives an AC signal from the sensing electrode and that analyzes the AC signal. ...


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USPTO Applicaton #: #20120086502
Inventors: Patrick G. Smith


The Patent Description & Claims data below is from USPTO Patent Application 20120086502, Device and method for monitoring an electrochemical gas sensor.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent application Ser. No. 12/056,876 filed Mar. 27, 2008, now U.S. Pat. No. ______, and incorporated herein.

BACKGROUND

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The invention relates to monitoring the function of an electrochemical gas sensor.

Many work place and production environments are monitored for the presence of potentially dangerous gas mixtures. Electrochemical gas sensors are often used to detect the presence of one or more gases in an environment. Electrochemical gas sensors usually give an electrical response that is proportional upon the concentration of the gas being detected. Electrochemical gas sensors include an electrochemical cell that includes a sensing electrode (which is also referred to as the working electrode), a counter electrode and an electrolyte. Some electrochemical cells also include a third electrode that is referred to as the reference electrode. An external voltage is applied to the reference electrode to bias the redox reaction. During cell operation, when a gas dissolves into the electrolyte, an oxidation reaction occurs at one electrode and a reduction reaction occurs at the other electrode. This is referred to as the “redox” reaction. Electrons flow from the oxidizing electrode to the reducing electrode. This electron flow (i.e., electrical current) is then measured, which measurement is then translated into the concentration of gas detected.

Electrochemical cells eventually fail due to a variety of causes including, e.g., the electrolyte drying up, the electrolyte becoming contaminated, and the electrodes becoming physically disconnected. In many cases, the failure goes unnoticed. Unfortunately, in many cases when failure occurs no current flows, which is the same thing that occurs when no gas is present in the system. In addition, in many failure situations, the cell becomes unresponsive to the target gas, i.e., the gas that the cell was designed to detect. As a result, the signal produced as a result of a failure is the same signal that is produced when gas is being detected (i.e., no current flow), and for this reason the failure may go undetected.

Various mechanisms are used to address the fact that electrochemical cells fail. In some cases, the cell has a fixed service life or a limited lifetime and the user simply disposes of the cell after a predetermined period of time and replaces it with a new one, regardless of whether or not the cell is still functioning. Some electrochemical cells are equipped with a gas generating cell that operates in reverse of the electrochemical cell. Rather than generating a redox current when gas is applied, it generates gas when current is applied. The gas generating cell is actuated periodically to determine the viability of the sensing cell. Other techniques rely on a calibration of the cell at fixed time intervals or a “bump” test. A bump test typically involves exposing the electrochemical cell to a test gas mixture for a period of time sufficient to activate the warning alarms and/or other modes of display that indicate that the instrument is responding correctly to the gas. The bump test is usually quicker than a calibration, but it still involves the expense of both time and test gas mixtures.

Many methods for testing electrochemical cells involve applying a DC test signal using a dedicated circuit, i.e., a circuit whose sole function is to generate and send the test signal. The dedicated test circuit is separate from the circuit that biases the electrochemical cell. Examples of such test circuits are described in U.S. Pat. No. 6,428,684 (Warburton).

It would be desirable to have a simple test that can be performed automatically without human intervention for determining whether or not an electrochemical cell is functioning properly. It would also be desirable if such a test could be performed without interrupting the gas detection function of the sensor and by the existing circuitry of the electrochemical gas sensor.

SUMMARY

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In a first aspect, the invention features an electrochemical gas sensor testing device that includes a signal generator that generates a multiplexed signal that includes a first test signal that includes alternating current (AC) and is free of a direct current (DC) component, and a second signal that includes a DC bias voltage, an electrochemical cell that includes a counter electrode, a sensing electrode, and an electrolyte, the counter electrode and the sensing electrode being in communication (e.g., electrical) with the electrolyte and each other, the counter electrode being in communication (e.g., electrical) with the signal generator to receive the multiplexed signal generated by the signal generator, and a processor that receives an AC signal from the sensing electrode and that analyzes the AC signal. In one embodiment, the device further includes a filter that transmits alternating current and blocks direct current. In another embodiment, the device further includes a filter that blocks alternating current and transmits direct current. In some embodiments, the device further includes a filter that blocks alternating current and transmits direct current and a filter that blocks direct current and transmits alternating current. In other embodiments, the processor instructs the signal generator to generate the test signal.

In one embodiment, the processor simultaneously analyzes a DC signal corresponding to the concentration of gas present in the electrochemical cell and the AC signal. In another embodiment, the processor compares a first AC signal that corresponds to the AC test signal to a second AC signal that corresponds to the AC test signal (e.g., a stored test signal corresponding to a test signal received at a point earlier in time that the second AC signal).

In some embodiments, a single signal generator generates both the AC test signal and the DC bias voltage. In one embodiment, the single signal generator is a potentiometer. In other embodiments, the single signal generator is a variable gain amplifier.

In another aspect, the invention features a method of testing an electrochemical gas sensor, the method including simultaneously applying an alternating current test signal and a direct current bias voltage to a counter electrode of an electrochemical gas sensor, the electrochemical gas sensor including a sensing electrode, an electrolyte, and the counter electrode, transmitting the AC test signal from the sensing electrode to a processor, analyzing the AC signal received by the processor, and determining whether or not the electrochemical cell is functioning. In one embodiment, the method further includes comparing at least one frequency of an AC test signal transmitted to the processor at a first time to the same at least one frequency of an AC signal transmitted to the processor at a second time later than the first time. In another embodiment, the method further includes simultaneously analyzing a DC signal corresponding to the concentration of a gas present in the electrochemical cell and the AC signal corresponding to the AC test signal.

In one embodiment, the processor simultaneously receives a DC signal corresponding to the concentration of a gas present in the electrochemical cell and an AC signal corresponding to the AC test signal.

In other embodiments, the method further includes storing a signal corresponding to the AC test signal. In another embodiment, the method further includes comparing a received AC signal corresponding to the AC test signal to the stored AC test signal. In one embodiment, the method further includes comparing a frequency of a received AC signal corresponding to the AC test signal to the stored signal (e.g., same frequency of the stored signal).

In some embodiments, when no AC signal is received by the processor, a signal is generated indicating that the cell is not functioning properly. In other embodiments, the AC test signal includes multiple frequencies. In one embodiment, the AC test signal includes constant frequency and amplitude.

In other embodiments, the method further includes applying the AC test signal continuously to the electrochemical cell.

In other aspects, the invention features an electronic circuit that includes an electrochemical cell, and a single signal generator that applies an AC test signal and a DC bias voltage to the electrochemical cell. In one embodiment, the signal generator applies the AC test signal and the DC bias voltage simultaneously to the electrochemical cell. In another embodiment, the signal generator is a variable gain amplifier. In other embodiments, the signal generator is a potentiometer. In another embodiment, the circuit further includes a processor that instructs the signal generator to generate the test signal.

The invention features the application of an AC test signal to an electrochemical cell of a gas sensor that does not interfere with the gas detection function of the sensor and that indicates whether or not a cell is working, failing or has failed. The invention also features a method of testing an electrochemical cell of a gas sensor where the method can be conducted at the same time the cell is detecting a gas of interest.

The invention also features the application of a multiplexed signal to an electrochemical cell of a gas sensor where the multiplexed signal includes both an AC test signal that is free of a DC component, and a DC bias voltage.

The invention features the ability to utilize the existing bias voltage circuit of an electrochemical cell of a gas sensor to apply a multiplexed signal that includes the AC test signal. Therefore the test method can be conducted without adding a separate test circuit. The invention also features a test signal that can be tailored to a particular cell\'s parameters.

Other features and advantages will be apparent from the following description of the drawings, the preferred embodiments, and from the claims. In the figures, like numbers are used to represent like elements.

BRIEF DESCRIPTION OF THE DRAWINGS

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FIG. 1 is a block diagram of an electrochemical gas sensor test device.

FIG. 2 is a schematic diagram of the electrochemical cell of the device of FIG. 1.

FIG. 3A is a schematic diagram of the electrochemical gas sensor test device of FIG. 1.

FIG. 3B is a schematic diagram of an electrochemical gas sensor test device that does not include a reference electrode.

FIG. 4 is a schematic diagram of an electrochemical gas sensor test device according to another embodiment.

FIG. 5 is a schematic diagram of another embodiment of an electrochemical gas sensor test device.

FIG. 6A is a graphical representation of a balanced step test signal (Vtest) applied to an electrochemical cell.

FIG. 6B is a graphical representation of the signal (Vo) at the output of a working electrochemical cell after application of the test signal (Vtest) of FIG. 6A.

FIG. 6C is a graphical representation of the fast Fourier transform of the output signal (Vo) of FIG. 6B.




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stats Patent Info
Application #
US 20120086502 A1
Publish Date
04/12/2012
Document #
File Date
12/31/1969
USPTO Class
Other USPTO Classes
International Class
/
Drawings
0




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20120412|20120086502|device and monitoring an electrochemical gas sensor|An electrochemical gas sensor testing device that includes a test signal generator that generates a multiplexed signal that includes a first test signal that includes alternating current (AC) and is free from a direct current (DC) component and a second signal that includes a DC bias voltage, an electrochemical cell |Sensor-Electronics-Corporation
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